Abstract
Enhancing the efficiency of heat transfer processes remains one of the key challenges in modern energy and thermal engineering. Conventional working fluids, such as water and ethylene glycol, are limited in terms of thermal conductivity and heat capacity, which reduces their potential under high heat flux conditions. One of the promising approaches is the use of nanofluids – suspensions of nanoparticles in a base liquid that can modify its thermophysical properties and improve heat transfer performance. This study presents a numerical investigation of the flow of water and TiO 2 -CuO nanofluid in a U-shaped tube channel under a constant heat flux. Computational fluid dynamics (CFD) was applied to analyze the distribution of turbulent kinetic energy (TKE), pressure variations along the channel, as well as integral heat transfer parameters: the heat transfer coefficient and heat absorption. The results showed that water exhibits higher turbulent activity, with maximum TKE values reaching 1.9·10 -3 m 2 /s 2 , while the overall pressure drop is about 230 Pa. Its relatively low thermal conductivity (0.6 W/m·K) leads to a temperature rise of 5-7 °C at the outlet. For the TiO 2 -CuO nanofluid, turbulence intensity decreases on straight sections (10 -6 -10 -5 m 2 /s 2 ) and the pressure drop increases up to 270 Pa due to higher viscosity. However, improved thermophysical properties – thermal conductivity (0.702 W/m·K) and density – ensure more effective heat removal, with outlet overheating reduced to 4-5 °C. Comparative analysis of heat absorption and the heat transfer coefficient revealed the advantage of the nanofluid: h=68.3 W/(m 2 ·K), Q=143 W compared with water (h=67.6 W/(m 2 ·K), Q=141.8 W). These results indicate that TiO 2 -CuO nanofluid provides higher heat transfer efficiency with an acceptable increase in hydraulic losses, making it a promising coolant for compact and high-load thermal systems.